The present invention relates to torsion damping devices, particularly for the friction plates of friction clutches.
It relates generally to torsion damping devices which comprise two coaxial parts mounted to rotate with respect to each other, within a predetermined range of angular clearance, namely one part comprising a web and another part comprising two annular guide members disposed one on each side of said web and connected to each other by cross-pieces parallel to the axis of the assembly, and a circumferential array of resilient means interposed between said parts of rotational connection thereof.
The present invention relates more particularly, but not exclusively, to torsion damping devices of the friction clutch plate with a so-called flexible center, particularly for a motor vehicle.
In such a friction clutch plate, one of the coaxial parts carries a friction disc, which is provided with friction linings at its periphery, on each of its faces, and which is thus adapted to be gripped between two members rotating with a shaft, in practice a driving shaft, whilst the other of said parts is fast with a hub, which is adapted to be engaged on another shaft, in practice a driven shaft.
Such a friction clutch plate insures controlled transmission of rotary torque between the part which rotates with a driving shaft and the other part which rotates with a driven shaft, i.e. filters audible vibrations which may, moreover, be produced along the whole kinematic chain in which said driving and driven shafts are interposed.
It is known to insert between the two coaxial parts of such a friction clutch plate, surface friction means adapted to introduce a hysteresis effect in the operating characteristics of said friction clutch plate; this hysteresis effect translates into a difference, for the same angle of clearance between the two coaxial parts of the friction clutch plate, between the value of the torque transmitted between these parts of a first direction of clearance, commonly known as forward direction, and the value of this torque transmitted for the opposite direction, commonly known as reverse direction.
It has proved, in fact, that for certain applications such a hysteresis effect contributes to a reduction of the vibrations and noise emitted by all the rotary members of the kinematic chain which includes the driving and driven shafts between which the clutch friction plate is interposed.
Depending on the operating characteristics to be obtained, at least part of the friction means may be used only for one portion of the predetermined range of angular clearance between the two coaxial parts of the friction clutch plate.
In any case, in the friction clutch plates of this type, the friction means are usually constituted by friction washers inserted axially between the web and one and/or the other of the annular guide plates along the inner periphery thereof.
This results in the internal structure of such a friction clutch plate being determined by its friction washers and in the hysteresis characteristics being associated with those friction washers.
Now, for certain particular applications, it is desirable to be able to adapt the hysteresis characteristics of such a friction clutch plate to the stiffness of its springs, this stiffness itself being chosen as a function of the conditions of use of the friction plate.
For the above reasons, such an adaptation has proved difficult, if not impossible, to the present time.